14.38 Magnetic Instruments

14.38.2 Given a sample deviation card, show how to apply corrections.

Compass Deviation;

• For a given aircraft compass, compass deviation is the angular difference between Magnetic Direction and Compass Direction caused by magnetic forces within the aircraft.

• It is expressed in degrees East (E) or West (W).

• The deviation can be reduced through a Compass Swing, typically to within a few degrees of error.

• A Deviation Card is displayed next to the compass, indicating which compass headings correspond to specific magnetic headings.

A simple phrase to remember is:

If Deviation is east, then Compass is least; 

If Deviation is west, then Compass is best.

If the Deviation is East,

• then the Compass direction will be less than the Magnetic direction.

example

2°E

If the Deviation is West,

• then the Compass direction will be more than the Magnetic direction.

example

2°W

14.38.4 Briefly:

(a) describe the construction of a present-day direct-reading compass;

• Consists of a magnetised element attached to a compass card
• The card is mounted on a pivot (jewel bearing) allowing free rotation
• Enclosed in a sealed bowl filled with liquid (for damping and stability)
• Mounted on a gimbal system to keep it level despite aircraft movement
• Includes compensating magnets to reduce deviation
• Fitted with a lubber line for reading heading
• Often has internal lighting for night use